The objective of this research is to develop and test a screening procedure for diagnosing the presence of renovascular hypertension which will (1) be non-invasive, involving only an arm vein needle puncture; (2) be totally risk free; (3) have greater sensitivity (low false negative rate) and greater specificity (lower false positive rate) than currently available non-invasive procedures; (4) be capable of diagnosing segmental as well as unilateral and asymmetric bilateral renovascular disease; (5) be simple to perform with no special training required; and (6) utilize equipment currently available in many hospitals. The procedure involves the acquisition of renal scan data with scintillation camera and processing of these data with a dedicated minicomputer. The output consists of (1) special "functional images" of the kidneys which will be far superior to conventional renal scan images in demonstrating renovascular disease, and (2) measurements of physiological parameters (clearances, transit times) related to split renal function (blood flow, urine flow and concentrating capability of each kidney). Computer processing is being completely automated. The procedure is being thoroughly tested on a large number of hypertensive patients as part of a strict and extensive protocol. It is anticipated that the procedure being developed through this research will prove to be the most informative non-invasive test for renovascular hypertension.